A large number of commercial and factory plant roofs are of a flat roof design wherein the roofing material itself is often of a built-up asphalt and in more modern systems of a single ply EPDM elastomeric sheet or membrane. In terms of securing a single ply EPDM membrane to the roof itself, one design utilizes a mechanical ballast system that uses a layer of stone over the membrane. While the ballast system is least expensive it has a disadvantage of being quite heavy (approximately 10 pounds per square foot) thus requiring a heavy roof support structure and in addition the roof slope cannot exceed 10%.
Adhered roof membrane retention systems suffer from the cost penalty while mechanical fasteners and related fastening systems generally require fixation to the roofing substrate via mechanical fasteners. There are two basic kinds of mechanical fasteners namely, membrane penetrating and non-penetrating ones. Each of these types of fasteners has a number of favorable features and each of them is also subject to various drawbacks and disadvantages.
Mechanical fastening systems of the penetrating type generally require fixation to the roofing substrate by a metal fastener with metal or rubberized nailing strips. U.S. Pat. Nos. 4,445,306; 4,074,501; 4,455,804; and 4,467,581 are examples of penetrating type fastening systems in which various rigid and semi-rigid members are used to secure the membrane to the roof. These systems require openings to be formed in the membrane either for receiving a fastening plate or by the attaching anchoring members.
Examples of a non-penetrating type fastener are shown in German Patent Publication No. 24 33 669 in which the membrane fastener comprises a lower disc which is attached to a roofing substrate by an anchoring member. The roofing membrane is fitted over the lower disc and an upper disc is snapped over the lower disc to perfect the fastening and exert a sealing effect. In another embodiment of this Patent Publication, a plug is driven into the upper disc to expand the body thereof into an annular space provided in the lower disc to anchor the upper disc thereto. Another type of non-penetrating fastening system is shown in U.S. Pat. No. 3,426,412 which has a flexible fastening cover which is snapped over a base member to trap the membrane therebetween. Another embodiment shown in this U.S. patent uses a plug-like member which is snap-fitted into a recess formed in a lower member which is rigidly connected to the roof to trap and clamp the membrane therebetween. U.K. patent application No. GB 2,060,752 shows another type of non-penetrating fastener for use for attaching flexible film to rigid frame members in the construction of a greenhouse or the like.
Still another type of non-penetrating fastener which is believed to be the closest to my invention is shown in U.S. Pat. No. 4,519,175. The fastener of this patent consists of a knobbed base plate which is anchored to the roof over which the membrane is placed. A stiff externally threaded retainer is formed by a plurality of separate skirt members and is snapped over the knob of the base plate securing the membrane to the plate. An externally threaded cap is screwed onto the retainer which clamps the skirt members about the knobbed top of the base plate. The retainer must be formed of a rigid plastic material in order to have the external threads formed in the outer surface thereof for cooperation with the internal threads on the locking cap. This stiff retainer occasionally will pinch the roof membrane resulting in a weak area in the membrane or can tear the membrane sufficiently to result in a leak. This recognized problem is apparently overcome by the use of a lubricant on the inner surface of the retainer which clamps against the membrane.
Although both the penetrating and non-penetrating type fastening systems do work satisfactory for many applications, it is desirable to have a non-penetrating system for certain applications to eliminate piercing the membrane. Also such a fastener can be installed in a minimum amount of time and without requiring skilled labor, and the fastening element can be securely retained in clamping engagement with the trapped membrane to reduce the accidental disengagement thereof upon the membrane experiencing severe uplift wind forces.
Another problem that exists with certain of the roof fastening systems and in particular the non-penetrating type is the relative ease by which vandals can remove the exposed locking component of the fastener. Although this is not a problem for many installations since the roofs are inaccessible to outsiders, it can be a problem for those buildings that are readily accessible and for buidings subject to vandalism such as schools. In most known prior non-penetrating fasteners, the locking cap or component can be pried off or unscrewed and removed easily without requiring special tools.